Railroad communication system

ABSTRACT

A radio communication control system for a lead unit and a plurality of remote units is disclosed. The system has a protocol for establishing a communication link between the lead unit and the one or more remote units in the system which prevents any of the units in that system from processing messages or commands from other units in other train systems or processing messages or commands originating from units within a train system which are addressed to other units within the system. The communication system also includes a communications channel contention system for minimizing the probability of multiple units transmitting on the common communication channel at the same time and for insuring that the highest priority communications in each train are transmitted first in time measured from the end of the latest transmission on the radio communications channel. The invention also includes apparatus for verifying the establishment of the communications link by means of signaling through the mechanical coupling in the train and monitoring the radio response. The invention further includes an improved flow rate sensor for use in a remote unit for determining when significant air flows occur into the brake pipe of the remote unit. The invention further includes an air pressure regulation system which prevents the fluctuation of the air pressure in the equalizing reservoir of the lead and remote units consequent from either leakage or change in the ambient temperature.

CROSS REFERENCES TO RELATED APPLICATIONS

This is a division of Application Ser. No. 143,118, filed 1/12/88, ofRichard E. Nichols et al for RAILROAD COMMUNICATION SYSTEM nowabandoned; which in turn is a Divisional application of U.S. Ser. No.747,504, filed June 21, 1985, now abandoned; which in turn is aDivisional application of U.S. Ser. No. 532,147 filed Sept. 14, 1983,now U.S. Pat. No. 4,582,286.

FIELD OF THE INVENTION

The invention relates to railroad radio communication systems forcontrolling one or more units or groups of remote units from a leadunit. The invention also relates to air brake systems for use in trainhaving one or more remote units or groups of remote units controlledfrom a lead unit in which information concerning the air flow into thebrake system at the remote units is monitored and analyzed, the resultof which is telemetered to the lead unit. The invention also relates toair brake systems for trains which are not susceptible to pressurechanges in the brake pipe system caused by temperature variations orleakage.

DESCRIPTION OF THE PRIOR ART

U.S. Pat. No. 3,380,399 discloses a train control system in which a leadunit controls the operation of one or more remote units throughcommunications transmitted between the lead unit and the one or moreremote units over a half duplex channel using frequency shift keying(FSK) to serially transmit control information regarding a plurality offunctions of the train. In that system, a total of 38 bits ofinformation are transmitted in each half duplex communication. The leadunit and each remote unit store a four bit address code which can beused to define sixteen addresses. The four bit address code is used todetermine if radio transmissions should be processed by any receivingunit by matching the address code contained in the received message withthat stored at the receiving unit. The use of a single common addressdoes not assure against the remote possibility that other units, inanother train in proximity to a receiving unit, are activated by thecontrol information being transmitted to the receiving unit or thatinformation transmitted by a remote unit is processed by the lead unitof another train. The system controls the time that transmissions aremade from various units within the same train in accordance with a fixeddelay.

Locomotive control systems are presently marketed which utilize thebasic concepts described in the U.S. Pat. No. 3,380,399. These systemsare improvements of the systems of U.S. Pat. No. 3,380,399. Such systemscontain a system for preventing the simultaneous transmission ofmessages by any one of a plurality of units within one or plural trainswithin transmitting range of each other. Simultaneous transmissions canat time under specific circumstances lock up the communications channelbetween various trains within transmitting distance of each otherthereby preventing effective command execution which can at timesinclude plural trains in proximity to a train yard. Present systemsnormally use a 62 ms delay between the time of receipt by a remote unitof transmissions from a lead unit to the time of transmitting a reply bythe remote unit transmission to the lead unit. These systems furtherinclude a delay time for the lead unit to transmit after thetransmission of another unit which is the sum of a one and one halfseconds plus an additional time determined from the twelve addressingbits currently used for the addressing of the lead and remote units in amanner analogous to that described above with reference to U.S. Pat. No.3,380,399. Thus, prior systems, while providing a non-fixed time periodbetween transmissions of different lead units did not contain an overalleffective system for accurately controlling when different remote unitscould reply to transmissions from a lead unit, nor a system havingdifferent time intervals for the transmission of various types ofmessages measured from the end of the last radio transmission. Suchsystems did not make any provision for assuring the transmission of thehighest priority messages first and transmitting messages of lesserpriority after the completion of the transmitting of the higher prioritymessages.

Prior air braking systems for trains having a lead unit which controlledone or more groups of remote units by a radio communication channelmonitored the flow of air in a flow adapter located between a mainreservoir and a brake valve relay section in the remote units. Twosensors were connected to the flow adapter such that the first sensorsensed the differential pressure across the flow adapter to determinewhen the pressure drop across the flow adapter was above a maximum levelindicative of a significant flow rate requiring idle down of the removeunit wherein idle down is the stepping down of the throttle to idle andcutting out of the air brake feed valve. The flow adapter was coupled toan accumulator. A choke was coupled between the accumulator and the flowadapter. The second sensor, which was a differential pressure switch,was connected across the choke for sensing when the pressure drop acrossthe choke exceeded a threshold. The accumulator functioned to hold thesame pressure as the pressure in the flow adapter during steady stateconditions. However, a rapid change in the flow rate between the mainreservoir and the relay valve causes a differential pressure to becreated across the choke which was sensed by the differential pressureswitch. Any rapid change in the flow rate (e.g. 5 psi pressuredifferential) could at times cause the differential pressure switch totrip. Any tripping of the differential pressure switch may beintrepreted as a condition resulting in the unnecessary idle down of theremote unit. The differential pressure switch was mechanical andfunctioned to produce an indication of any threshold differentialpressure greater than its sensitivity during a time interval greaterthan its response time capability. Effectively, the differentialpressure switch functioned almost instantaneously to produce an outputsignalling a rapid flow rate into the brake pipe. The differentialpressure switch was at times susceptible to being tripped by transientconditions such as those that might occur when a train is being pulledout of the yard in the morning under conditions of extreme cold when thevarious air fittings of the brake pipe are being stressed. These shorttransient air flows do not warrant the idle down of the remote unit.

Prior air brake system utilized an unregulated equalizing reservoir forsustaining the pressure in the train brake pipe during application ofthe air brakes. Once the air brakes were applied, the equalizingreservoir was shut off from the pressure regulated main reservoir whichleft the equalizing reservoir in an unregulated air pressure state.Without application of a regulated source of air to the equalizingreservoir, certain conditions can cause the variation of the pressure inthe equalizing reservoir from that which was applied during theinitiation of braking. Variation of the pressure in the equalizingreservoir can lead to either the increase or decrease of the brakingaction from that which was desired. If a train were traveling into atunnel where the temperature was warmer than the ambient temperature ofthe equalizing reservoir, the warmer temperature of the tunnel can attimes cause heat to flow into the equalizing reservoir to cause a risein pressure sufficient to tend to cause the brakes to decrease. If thetrain were going downhill while traveling into the warmer tunnel, theincrease in pressure in the equalizing reservoir could be translated bythe relay valve into a release of the brakes which could result in adecrease in the ability to properly control the train. If a train wastraveling into an area where the ambient temperature was colder than thetemperature of the equalizing reservoir, such as a tunnel in thesummertime, the pressure in the equalizing reservoir could drop with theflow of heat out of the equalizing reservoir. A pressure drop in theequalizing reservoir could at times cause the brakes to be appliedharder which could lead a decrease in the ability to properly controlthe train within the tunnel. Restarting of the train could requireextensive preparations.

SUMMARY OF THE INVENTION

The present invention is a radio control system for trains having a leadunit and one or more remote units or groups of remote control units inwhich the control functions of the one or more units or groups of remoteunits are controlled by radio commands from the lead unit. Theterminology "unit" as used herein describes both single and groups ofdiesel-electric units as well as single and groups of electricallydriven units and control cars which do not supply driving power to thetrain and which are used to control units. The radio communicationchannel between the lead unit and the one or more remote units alsosignals responses by the remote units to the commands from the leadunit. In addition, alarm conditions which occur in the remote unitswhich should be brought to the attention of the engineer in the leadunit are also sent to the lead unit to insure accurate train operation.

An aspect of the invention is an improved means of communication betweenthe lead unit and the one or more groups of remote units which providesincreased communication security over that realizable with the systemdescribed in U.S. Pat. No. 3,380,399 and the previous marketd radiocommunication systems. The radio communication system of the presentinvention prevents the activating of remote units associated with aparticular lead unit by radio communications emanating from a lead unitassociated with another train. A functional radio communications linkbetween a lead unit and a remote unit is not established until uniqueaddressing information has been exchanged between the lead unit and theremote unit and comparisons have been made therewith. These exchangesand comparisons greatly reduce the likelihood of an undesired functionalcommunications link being established between a lead unit in one trainand a remote unit in another train by the automation of theestablishment of the radio communications link which reduces thelikelihood of human error. Alternatively, the function of the lead unitmay be performed by a control tower when it is desired to control one ormore trains from a central location such as in the vicinity of a trainyard during train loading and unloading. After the initial establishmentof a communications link between a lead unit and a remote unit or tower,all further communications contain different unique addressinginformation than that used to establish the communications link whichfurther lessens the likelihood of undesired communications occurringbetween different units.

A further feature of the invention includes the use of the mechanicalcoupling such as the air brake pipe between the lead unit and the remoteunit to assure that a proper communications link has been established asfurther measure that control of the remote unit is at least in partinhibited unless the mechanical connection has been established orverified. For of the remote units is transmitted via the communicationschannel to the lead unit. Upon receipt of an acceptable response, thecontrol of lead unit can thereafter be enabled.

A further element of the present invention is designed to optimize thechannel use of the same radio carrier frequency by one or more trainswithin radio communication distance of each other. Interference betweenmultiple trains within radio communication distance of each other isminimized by establishing fixed control time intervals after the endingof the last radio transmission on the radio communication channel foreach individual remote unit to reply to a lead unit and a plurality ofnon-overlapping random time intervals following the initial timeintervals for transmitting various categories of commands or alarmconditions on the radio communication channel. The combination of fixedtime intervals for remote units to respond to commands from the leadunit and random time intervals for transmitting other informationminimizes the probability of more than one unit in the same train orunits in different trains from broadcasting on the same channel at thesame time. Alternatively, the time intervals for the remote units toreply to a command from a lead unit may be assigned randomly by a randomnumber generator contained in a microprocessor controller of each unitstation.

A communication system in accordance with the present invention for usewith the control of a railroad train having at least a lead unit and oneor more remote units in which the lead unit controls the operation ofthe one or more remote units with messages which are transmitted by aradio communication message between the lead unit and the one or moreremote units and the one or more remote units transmit return messagesto the lead unit confirming execution of the lead messages and messagesconveying information of the operation of the one or more remote unitscomprises a plurality of transceivers each adapted for location at adifferent one of the lead and one or more remote units for transmittingand receiving messages over the radio communication channel; a leadstation adapted for location at the lead unit, the lead station havingmeans for storing a first lead identifier which uniquely identifies thelead unit and a plurality of first remote identifiers equal in number tothe number of remote units or groups of units, each remote identifierbeing assigned to each remote unit for uniquely identifying that remoteunit and means for generating a common link message for all remote unitsor individual link messages for single remote locmotives, a link messageto be transmitted by the lead unit transceiver for establishing acommunication link between the lead unit and any specified one of theone or more remote units over which commands and messages conveyinginformation are to be transmitted, the link message containing theunique first identifier of the lead unit and the first unique identifierof the specified one of the remote units to which the lead unit is to belinked; and one or more remote stations adapted for location at each ofthe remote units, each remote station having means for storing itsassigned first remote identifier and the first lead identifier whichuniquely identifies the lead unit, means for comparing any received linkmessage to detect when a received link message contains a first leadidentifier and a first remote identifier which agrees with the firstlead identifier and first remote identifier stored at the remote stationreceiving the link message; and means for generating a link replymessage to each received link message when the comparison of thereceived first identifiers and the stored first identifiers by theremote station comparing means is in agreement, the link reply messagecontaining the first lead identifier and the first remote identifierstored at the remote station at which the comparison was in agreement,each remote station means for generating the link reply message beingcoupled to its associated transceiver for causing transmission of thegenerated link reply message. The first identifier can, for example, beentered into the communication system as part of the preparation set upsequence or automatically when combining the radio equipment with theunit.

The communication system further includes means located at the leadstation for comparing the stored first unique lead identifier and thestored one or more remote first unique identifiers with the first uniquelead identifier and the first unique remote identifier contained in anyreceived link message for detecting when the identifiers agree; andmeans for generating a message for transmission to the remote unit whichtransmitted the link reply message when agreement of the stored andreceived first unique identifiers is detected whereby a communicationlink is established between the lead unit and the remote unittransmitting the link reply message.

Further in accordance with the invention, the lead station means forstoring stores a second unique identifier of the lead unit and a secondunique identifier of each of the one or more remote units; each of theremote station means for storing stores a second unique identifier ofthe lead unit with which the remote unit is to be associated and its ownunique second identifier, the lead station means for generating a linkmessage includes the stored second unique identifier of the lead unit inthe link message; and each of the remote station means for generating alink reply message includes the stored second unique identifier of theremote unit in the link reply message. The second identifier can, forexample, be a code that is built into the transmitter portion of thecontrol system.

The lead station of the communication system of the present inventionalso includes means for generating messages for transmission to any oneof the one or more remote units, each message occurring after theestablishment of a communication link by the generation of the linkmessage and the link reply message, each message containing the secondunique identifier of the lead unit transmitting the message as the onlyidentifier of the lead station transmitting the message; messageprocessing means for processing any commands or messages received from aremote unit; and means for comparing the second unique identifier of aremote unit contained in each message received by the lead unittransceiver with the stored second unique identifier of the one or moreremote units and upon agreement of the identifiers coupling the receivedmessage to the message processing means located at the lead station.

Each of the remote stations of the present invention further includesmeans for generating messages for transmission to the lead unit, eachmessage occurring after the establishment of a communications link bythe generation of the link message and the link reply message, eachmessage containing the second unique identifier of the remote unittransmitting the message; message processing means for processing anyreceived commands or messages; and means for comparing the second uniqueidentifier of a lead unit contained in each message received from a leadunit with the stored second unique identifier of the lead unit and uponagreement of the lead identifiers coupling the message to the messageprocessing means located at the remote unit station.

The first unique identifier of the lead unit is preferrably a numberused to identify the lead unit by a railroad operating the lead unit;the first unique identifier of each of the one or more remote units ispreferrably a number used by a railroad operating each of the one ormore remote units; the second unique identifier of the lead unit ispreferrably a number which is used to identify the lead station; and thesecond unique identifier of each of the one or more remote units ispreferrably a number which is used to identify that remote station.Preferably the second unique identifiers of the lead and remote unitsare the serial numbers of the respective lead and remote stations.

Alternatively, a second unique identifier of the lead unit and thesecond unique identifiers of the one or more remote units may begenerated respectively by random number generators located at each ofthe units. The randomly generated second unique identifiers areprocessed by the system in the same manner as the non randomly generatedsecond identifiers.

Further in accordance with the invention, the lead and one or moreremote units may be assigned a common third identifier which is storedby the lead and remote station means for storing; the lead station meansfor generating a link message includes the stored third identifier inthe link message; each of the remote station means for generating a linkreply message includes the stored third identifier in the link replymessage; the lead station means for comparing compares the stored thirdidentifier with the third identifier in any link reply message to detectwhen the third identifiers agree; the remote station means for comparingcompares any received link message to detect when a received linkmessage contains a third identifier which agrees with the thirdidentifier stored at the remote unit receiving the link message; and theremote station means for generating the link reply message to each linkmessage generates the link reply when the remote unit means forcomparing signals that all of the stored and received identifiers agree.Preferably, the third identifier is an eight bit version code which isused to distinguish different message formats associated with types ofoperation, e.g. diesel or electric unit operation.

The present invention also includes lead and remote stations which areused in the above described communication system.

The present invention includes a system for controlling which unittransceiver transmits on the radio communication channel. Thetransmission control system includes means adapted for association witheach transceiver in the system for detecting the ending of atransmission on the channel by any transceiver; and means adapted forassociation with each of the transceivers which is responsive to anassociated means for detecting for controlling the initiation of atransmission after the ending of a previous transmission. Each of theone or more remote transceivers is assigned a time interval measuredfrom the end of the latest transmission for initiating a reply to anylead unit transmission, each time interval for the transmission by theremote units being non-overlapping with the time interval for the otherremote units. Alternatively, each remote station may be assigned a timeinterval for initiating a reply to any lead unit transmission by arandom number generator.

Further in accordance with the system for determining transmission onthe radio communication channel, one of the remote units functions as afirst repeater for receiving a transmitted message from the lead unitand retransmitting that message; and the repeater is assigned a timeinterval measured from the end of the latest transmission for repeatingthe transmission by the lead unit which is identical to one of the timeintervals of the remote units for transmitting replies to transmissionsfrom the lead unit or the reply message from the remote.

A system for controlling which unit transmits on the radio communicationchannel further includes a transceiver associated with a second repeateradapted for a location off of a train for receiving a transmission froma lead unit and retransmitting that transmission and wherein the meansadapted for association with the transceiver of the second repeater forcontrolling the initiation of transmission by the second repeater isassigned a time interval for repeating the transmission which does notoverlap the time intervals of the remote units for transmitting repliesto transmissions from the lead unit and follows the time interval of thefirst repeater for initiating retransmission of a transmission of thelead unit or the remote unit reply message.

Further in accordance with the system for controlling which unittransmits on the radio communication channel, a plurality of timeperiods are assigned for transmitting different groups of commands afterthe latest transmission on the radio communication channel. The actualtime of transmission of a command within each of the time periods isassigned randomly by a random number generator.

The present invention is an apparatus for measuring air flow ratebetween a main reservoir and a relay valve in a remote unit. Theapparatus for measuring air flow rate is used in a train having at leasta lead unit, one or more remote units and a plurality of cars which areprovided with air brakes, the remote units each having an equalizingreservoir for providing a pressure reference for air brake control and arelay valve in communication with the equalizing reservoir for applyingpressurized air equal in pressure to the air pressure in the equalizingreservoir to a brake pipe coupled to the air brakes for the activationand deactivation of the air brakes of the plurality of cars; a mainreservoir of air coupled to each relay valve for charging the brake pipewith air; and means disposed between the main reservoir and the relayvalve for sensing the rate of flow of air between the main reservoir andthe relay valve. The apparatus for analyzing flow rate between the mainreservoir and the relay valve comprises means for measuring the pressuredrop across the means for sensing flow rate, the means for measuringhaving a response time for sensing any change in pressure drop; andmeans for analyzing the pressure drop over a time interval longer thanthe response time to detect a characteristic of the pressure drop as afunction of time which is indicative of a flow rate change across themeans for sensing. The means for analyzing detects when the pressuredrop across the means for sensing flow rate exceeds a predeterminedthreshold pressure. The means for analyzing can utilize differentmethods of analysis of the pressure drop over the time interval. Thesemethods, without limitation of the invention thereto, may (1) integratethe change in pressure drop as a function of time from the beginning ofthe time interval to the end of the time interval and signal when thevalue of that integration exceeds a threshold; (2) average the rate ofchange of pressure drop from the beginning of the time interval to theend of the time interval and signal when the value of that averageexceeds a threshold; and (3) average the rate of change of the pressuredrop during a plurality of sub time intervals within the time interval,and signal when a predetermined number of the averages during the subtime intervals consecutively exceed a threshold.

The apparatus for analyzing flow rate between the main reservoir and therelay valve may be used in an air brake system for a train having acommunication channel in which each of the remote units are controlledfrom the lead unit and each of the remote units transmits messages tothe lead unit in response to commands and to the occurrences of alarmsin the remote unit. Each remote unit has a transceiver; and meanscoupled to each of the means for analyzing flow rate for causing theremote transceiver to signal the lead unit transceiver when either (1)the pressure drop exceeds the predetermined threshold pressure drop or(2) the analysis of the pressure drop over a time interval exceeds apredetermined threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system schematic view of a train utilizing the presentinvention.

FIG. 2 is a system schematic of a modification of the system of FIG. 1.

FIG. 3 is a schematic view of an individual station used in the systemof FIGS. 1 and 2.

FIG. 4 is an electrical schematic of the electronics module of FIG. 3.

FIG. 5 is a schematic of the flow rate analyzing apparatus of thepresent invention.

FIG. 6 is a schematic of the pressure regulated equalizing reservoir ofthe present invention.

FIG. 7 is a flow chart illustrating the organization of the varioussubroutines which the microprocessor controller executes in the presentinvention.

FIG. 8 is a flow chart of the lead unit function control program.

FIG. 9 is a flow chart of the lead unit automatic brake function controlprogram.

FIG. 10 is a flow chart of the remote unit function control program ofthe present invention.

FIG. 11 is a flow chart of the remote unit automatic brake functioncontrol program.

FIG. 12 is a program illustrating the sequence of communications whichoccur during the establishing of a communications channel between a leadunit and a remote unit.

FIG. 13 is a flow chart of the sequence of communications which occurwhen the continuity of the brake pipe is checked.

FIG. 14 is a diagram illustrating the response of the pressuretransducer of FIG. 5 as a function of time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. General System Description

FIGS. 1 and 2 schematically illustrate a communication system 10 whichis used for controlling one or more remote units 12 from either a leadunit 14 (FIG. 1) or control tower 16 (FIG. 2) with a single FMhalf-duplex communication channel having a three kHz band width. Theindividual radio transmission contain a serial binary code which hasbeen FSK encoded. The details of the control functions and thetransmission format of individual messages are discussed in detail infrain section V. It should be understood that the only differences betweenthe systems of FIGS. 1 and 2 are that the function performed by the leadunit 14 of FIG. 1 is replaced by the control tower 16 in FIG. 2 andcertain interlocks of the system of FIG. 1 are eliminated. Specificallythere interlocks are (1) the usage of a lead unit first uniqueidentifier, (2) the requirement for a five psi rise in brake pipepressure to permit feed valve cut in, (3) the elimination of the brakepipe continuity test, (4) the communications interruption time intervalis shortened from 45 seconds to 30 seconds and (5) communicationsinterruption results in a full automatic brake application in additionto idle down of the remote unit. Additionally, the control tower is notassigned a first unique identifier, but is assigned the second uniqueidentifier. Hereinafter, the term lead station 30 is used to describeboth the lead station 30 in the lead unit 14 of FIG. 1 and the leadstation 30 of the control tower 16 of FIG. 2. The train 18 has inaddition to the lead unit 14 and one or more remote units 12, aplurality of cars 20 which separate the lead unit from the remote unit#1 and the remote unit #1 from the remote unit #2. The cars 20 areprovided with an air brake system which functions to apply the airbrakes upon a pressure drop in the brake pipe and to release the airbrakes upon a pressure rise. The details of the air brake system aredescribed infra in section IV. The individual cars 20 are coupledtogether by a brake pipe 22 which conveys the air pressure changesspecified by the individual air brake controls 24 in the lead unit 14and the remote units 12. An off board repeater 26 may be disposed withinradio communication distance of the train 18 for relaying communicationstransmitted between the lead unit 14 and one of the remote units 12. Theoff board repeater 26 would typically be used in a situation wheredirect communications between the lead unit 14 and the remote units 12are hampered such as while the train 18 is within a tunnel. The leadunit 14, the remote units 12 and the off board repeater 26 and thecontrol tower 16 are provided with a transceiver 28 which functions toreceive and transmit the FM communications on the half duplexcommunications channel. The lead unit transceiver 28 is associated witha lead station 30 which contains the electronics for the control of theremote units 12 by the lead unit 14. Each of the remote units 12 and theoff board repeater 26 has a remote station 32 which contains theelectronics for responding to the transmissions of the lead stationtransceiver 28. Both the lead station 30 and the remote stations 32 areadded on to the conventional unit. Additionally, the roles of the leadstation and remote station may be interchanged by the selection of anappropriate control made on the control console 34 (FIG. 3) of the leadstation 30 and the control console of one of the remote stations 32. Thecontrols on the control console 34 are not illustrated. Each of the unitcontrol consoles 34 is coupled to an associated air brake console 44(FIG. 3). The lead station 30 and the remote station 32 each include anair brake control 78 (FIG. 5) which controls the train air brakes Thedetails of the lead station 30 and the remote station 32 are describedinfra with regard to FIG. 3. It should be understood that the airbraking system used with the invention as illustrated in FIGS. 1 and 2is of conventional design with the exception of the subject matterdescribed infra with regard to FIGS. 5 and 6.

II. General Description of Security System

The present invention provides a security system which prevents unitsassociated with different trains from communicating with each other andunits in the same train from communicating with each other when in factcommunication with another unit in the same train was desired. Thesecurity system utilizes two unique identifiers and a third commonidentifier for each of the lead unit 14 and the one or more remote units12 during the establishment of the communication links between the leadunit and the remote units. The security system also includes averification scheme via the train mechanical coupling between the leadunit 14 and the one or more remote units 12. The sequence ofestablishing communications links between the lead unit 14 and each ofthe one or more remote units 12 is described hereinafter in conjunctionwith the "link" and "link reply" messages. Each of the stations 30 and32 stores the first and second unique identifiers which identify theunit with which that station is associated and the unique code assignedto that station. The stations 30 and 32 also store the common thirdidentifier which may be referred to as a version code and preferrably isused to identify different message formats associated with differenttypes of train operation such as diesel or electric. The first uniqueidentifier is preferably the four digit number assigned by the railroadto identify a unit and is typically visible to the engineer operatingthe unit. The second unique identifier is preferably the serial numberof the lead station 30 when a lead unit is being identified and ispreferably the serial number of the remote station 32 when a remote unitis being identified. The lead station 30 initiates the establishment ofa communications link between the lead unit 14 and one of the remoteunits 12 by the transmission of a link message. The link messagecontains the first and second unique identifiers of the lead unit 14 andthe first unique identifier of the remote unit 12 to which the lead unitwishes to link for establishing a communication link and the versioncode. The remote unit 12 to which the lead unit 14 wishes to linkreceives the transmitted link message and compares the transmitted firstunique identifiers of the lead unit and the remote unit and thetransmitted version code with the stored first identifiers and thestored version code to determine if they agree. If the first identifiersand the version code do not agree, the receiving remote station 32 doesnot consider the transmitted message to be a request to create acommunications link with the lead unit transmitting the link message. Ifthe comparison of the first unique identifiers and the version codecontained in the link message agrees with those stored at the receivingremote station 32, the receiving remote station saves the second uniqueidentifier which was transmitted as part of the link message for its uselater on as the addressing mechanism for transmitting messages to thelead unit 14. After all of the required comparisons have been made atthe receiving remote station 12, the remote station transmits a linkreply message which contains the first identifiers of the transmittingremote unit and the lead unit to which the link reply message is to betransmitted and the version code. The link reply message also containsthe second unique identifier of the remote station 32 transmitting thelink reply message. The lead unit 14 compares the first identifierscontained in the link reply message with the first identifiers stored inthe storage of the lead station 30 and the transmitted version code withstored version code. If there is agreement between the transmitted firstidentifiers, and version code with the stored first identifiers andversion code, the storage of the lead station 32 stores the secondunique identifier contained in the link reply message for use as theaddress of the remote unit 12 transmitting the link reply message. Allfuture communications between the lead unit and that remote unit 12 usethe second unique identifier to determine if received messages aretransmitted from that remote unit. After the storage by the lead station30 of the second unique identifier contained in the link reply message,confirmation of the establishment of the communication link is signaledwhen the lead unit 14 transmits a command to that remote unit 12 whichoccurs a minimum of every twenty seconds.

As a further feature of the security system, the lead unit can signalthe remote units via the mechanical coupling to verify, through thephysical connection, that the remote units are properly linked forcommunication. More specifically, the lead unit 14 can signal, theremote unit 12 via an air brake connection in the mechanical coupling.The signal can, for example, be an increase, or decrease in airpressure, or perturbations in air pressure, although for this specificexample a decrease in the air pressure is preferred. The remote station32 is adapted to detect such signal and send a message, along with theappropriate identifier to the lead unit. If all remote stations do notreply within a specified time, the lead and/or remote locomtives areinhibited from using the remote unit as part of the power drive for thetrain.

III. Stations

FIG. 3 illustrates a schematic view of one of the stations 30 or 32which are interchangable in function by the activation of a suitablecontrol (not illustrated) on the console 34 of the station. The console34 contains a plurality of controls and alarms, which are controlled byprogrammed microprocessors located in each station. Each station has atransceiver 28 which receives communications on the FM communicationchannel and transmits communications originating with the unit withwhich the station is associated. The transceiver is coupled to anelectronics module 36 which is illustrated in detail in FIG. 4. Thestation console 34 is coupled to an air brake console 44 which containsthe controls for various air brake controls used on units. Aninput-output module 46 is coupled between the electronics module 36 andan interface module 48. The interface module 48 is coupled to an airbrake manifold 50. The interface module functions to convey signalsbetween the air brake manifold 50 and the electronics module 36 forprocessing by the microprocessor located in the electronics module andfor transmission to the console 34 for display.

FIG. 4 illustrates a schematic of the electronics module 34 of FIG. 3.The electronics module includes a data bus 52 which functions totransmit digital communications throughout the electronics module. Aprocessor board 54 is coupled to the data bus. The processor board 54includes the programmed microprocessor which controls the system.Preferably, the microprocessor is a National Semiconductor CorporationNSC 800. The processor board 54 also includes random access memory(RAM), programmable read only memory (PROM), serial input-outputcapability and parallel input-output capability. The serial input-outputcapability is used for printing maintenance data. A panel 56 for aremote unit is provided, which contains the unit number switches forstoring the number of the lead unit to which the remote unit containingthe station is to be linked, and various diagnostic indicators. For alead unit, switches and indicators are provided on a console for settingthe number(s) of the remote units to which the lead unit containing thestation is to be linked. The unit number in the lead unit switches maybe manipulated by the engineer who is operating the lead unit 14 and inthe remote units 12 by the personnel setting up each of the remote unitsfor linking to the lead unit. The PROM stores the second uniqueidentifier of the station with which it is associated. The PROM alsostores the third identifier which is the common version code. Theversion code is preferrably an eight bit number used for differentiationbetween different message formats associated with different types ofoperation such as diesel and electric primary power, etc. The data bus52 is also coupled to a communications board 58 which includes aplurality of UART's (Universal Asynchonous Receiver Transmitter) amodem, radio keying circuitry for controlling the FM carrier,input-output, and watch dog timers which are used for various processorand system activities. The communications board is coupled to anassociated transceiver 28 and to the console 34 and receives inputs fromthe unit to which the station is associated. The bus 52 is also coupledto an input-output board 60. The input-output board includes an A to Dconverter, a multiplexer, D to A converters and parallel input, and/oroutputs. The input-output board 60 receives inputs from the unit andsupplies outputs to relay drivers, to electric brakes, and to the airbrake control board 62 and other control items. The air brake controlboard 62 is coupled to relay drivers.

IV. Air Brakes

The following air brake functions are present in the air brake system ofthe train 18 in FIG. 1.

A. Feed Valve

The remote automatic brake charging and venting is controlled via aremote feed valve function. The feed valve is cut in by:

1. Placing the system in a mode other than isolate mode.

2. Pressing the feed valve in button (not illustrated) on the air brakeconsole 44.

3. Pulling the automatic release button (not illustrated) on the airbrake console 44.

4. Charging begins after a 5 psi rise in remote brake pipe pressure issensed.

The remote feed valve may be cut out by moving a mode rotary switch tothe isolate position.

The feed valve control signal is a binary pneumatic output at the remoteunits 12.

B. Automatic Brake

Lead unit and remote unit automatic air brake functions are controlledfrom the air brake console 44. An automatic brake application isinitiated by pressing the automatic application button (not illustrated)on the air brake console 44. The pressures in the lead and remoteequalizing reservoirs 82 are reduced equally so long as the button ispressed. The minimum reduction is 7 psi for a first reduction and is 2psi after the first reduction.

An automatic release is initiated by pulling the automatic releasecontrol on the air brake console 44. This causes the lead unitequalizing reservoir pressure to increase to the pressure set by thelead automatic air brake regulating valve 86 (FIG. 5). The remote unitequalizing reservoir similarly increases to the pressure set by itsregulating valve. The automatic release function also releases emergencyapplications.

The automatic brake control signal is an analog pneumatic output at thelead and remote units. A binary pneumatic output and pressure switchperforms the emergency reset function at the lead and remote.

C. Independent Brake

Lead unit independent brakes are controlled from the air brake console44 and from the lead unit independent brake valve (not illustrated). Thelead unit brake cylinder pressure will be equal to the greater of thetwo control pressures. The remote unit independent brakes are controlledfrom the lead unit air brake console 44.

An independent brake application is initiated by pressing theindependent application button (not illustrated) on the air brakeconsole 44. This causes the independent brake control pressure at thelead and remote units to increase, so long as the button is pressed.

An independent brake release is initiated by pressing the independentrelease button on the air brake console 44. The lead and remote unitindependent brakes are reduced to zero and an actuating pipe ismomentarily pressurized. The independent brake valve may be used tooverride a pushbutton independent release at the lead unit.

The independent brake control signal is an analog pneumatic output atthe lead and remote units. The independent actuating signal is a binarypneumatic output at both the lead and remote units.

D. Emergency Brake

An emergency brake application can be initiated in any of three methods:

1. Pressing the emergency button (not illustrated) on the air brakeconsole 44. This causes electric valves to operate at the lead andremote units which cause the braking action.

2. Causing a brake pipe emergency at the lead unit. This is sensed by apressure switch connected to the A-1 charging cut-off pilot valve (notillustrated). The electric valves at the lead and remote units operateas above.

3. Pressing the emergency button on the air brake console 44. A manualvalve in the console initiates a brake pipe emergency which is sensedand propagated as in (2) above.

An emergency application is released by pulling (unlatching) the button,then after three minutes pulling the automatic release button.

An emergency application sensed at the remote unit is reported by thecommunications channel to the lead unit but not duplicated there.

A major system failure or battery power interruption results in aemergency brake application and automatic unlinking described infra inthe section V.

In the unlinked mode, all remote control functions are disabled, and theemergency brakes are applied.

The emergency brake control signal is a binary pneumatic output at boththe lead and remote units. The brake pipe emergency status signal is abinary pneumatic input at both units.

E. Air Brake Function Interlocks

Interlocks are included in the air brake control system to protectagainst improper operation.

1. Feed Valve Sequencing:

To cut in the remote feed valve, a mode select switch (not illustrated)is set in the isolate position. It is put in isolate when the feed valvein button on the system console 34 is pressed and then the automaticrelease switch on the air brake console 44 is pulled. The feed valve iscut in following a 5 psi rise in brake pipe pressure.

The remote feed valve is cut out by, setting the mode switch on thesystem console to the isolate position.

2. Minimum Automatic Reduction:

The minimum initial automatic reduction is 7 psi. The minimum additionalreduction is 2 psi.

3. Minimum Brake Pipe Pressure:

To prevent the loss of emergency brake capabilities, an automaticapplication below 45 psi is not allowed. If a reduction of brake pipepressure below 45 psi is attempted, an emergency application isinitiated by the system.

4. Automatic application/communication check interlock with override:

If the system includes override capability, a heavy brake application isrequired to idle down the remote unit following a communicationinterruption. Any automatic brake application under these conditions isconverted to a 10 psi (minimum) application.

If no remote reply is received within 5 seconds of an automaticapplication, a 10 psi application is generated by the system.

5. Automatic Application/Remote Changing flow display:

If an automatic brake application is made before the remote has fullyre-charged the brake pipe (as determined by the air flow rate), an airflow display (not illustrated) flashes and air audible alarm pulsesoccur.

6. Automatic Application/Remote Changing interlock option:

If an automatic brake application is made before the remote has fullyre-charged the brake pipe 22 (as determined by the air flow rate FIGS.5), the system adjusts the equalizing reservoir pressures at both leadand remote units to assure an effective brake. These pressures are setsuch that the brake application at the remote is the applicationrequested by the operator. This results in a heavier "effective" brakeat the lead.

FIG. 5 illustrates the aspect of the present invention which senses theair flow between a main reservoir 64 and a relay valve 66 by adifferential pressure transducer 68 which is coupled across a flowadapter 70 that is disposed between the main reservoir and the relayvalve. The flow adapter 70 is a choke having reduced diameter comparedwith the conduits coupling the one side of the flow adapter to the mainreservoir and the other side of the flow adapter to the relay valve 66.The differential pressure transducer 68 produces an analog outputvoltage which is coupled to the microprocessor contained within theprocessor board of FIG. 4. The analog output signal of the pressuretransducer 68 is converted to digital format and processed by themicroprocessor. The microprocessor detects differential pressures whichexceed a maximum threshold value under even transient conditions andperforms an analysis over a time period longer than the response timeperiod of the pressure transducer for determining abnormal flowconditions indicative of significant air flows into the brake pipe 22.The particular types of analysis performed by the microprocessor over atime interval longer than the response time of the pressure transducer68 may be in accordance with any known averaging technique whicheliminates the shutdown of a train solely in response to transientconditions having a magnitude less than the aforementioned maximumthreshold value. The function of the pressure transducer 68 is alsodiscussed infra with regard to FIG. 14. An automatic brake manifold 74is coupled to the relay valve 66 by a conduit 76. The automatic brakemanifold 74 is also coupled to an automatic brake valve 78 via conduit80. The automatic brake valve is coupled to the main reservoir 64 via aregulating valve 86. An equalizing reservoir 82 is coupled to the relayvalve 66. The equalizing reservoir 82 functions to translate pressuredrops and rises commanded from the lead unit 14, by activation of valvesin the automatic brake manifold 74 (FIG. 6), to the relay valve 66 whichapplies the pressure of the equalizing reservoir 82 to the brake pipe 22to maintain desired braking action. In the prior art air brake system,the application of an automatic brake command by the automatic brakevalve 78 or brake manifold decoupled the equalizing reservoir 82 from asource of pressure regulated air which permitted the pressure of theequalizing reservoir to vary as a function of the ambient temperature ofthe equalizing reservoir and from leaks in the equalizing reservoir.

FIG. 14 illustrates a typical output of the differential pressuretransducer 68 of FIG. 5 as a function of time. The programmedmicroprocessor analyzes the pressure drop across the flow rate adapter70, which is outputted by the pressure transducer 68 over a timeinterval longer than its response time to detect a characteristic of thepressure drop as a function of time which is indicative of a flow ratechange across the flow rate adapter. The microprocessor is programmedusing conventional programming techniques which do not constitute partof the invention. Whenever (including transients) the differentialpressure exceeds the threshold identified by reference numeral 84, themicroprocessor program immediately produces a flow rate alarm signal.This maximum pressure threshold 84 is indicative of a high rate of flowfrom the main reservoir 64 into the relay valve 66 which constitutes acondition requiring idle down. The transient 83, which is below thethreshold 84 will not activate the flow rate alarm when the time averageis above a second threshold. A transient 85 above the maximum thresholdpressure 84 does not have to be present for any period of time totrigger the flow rate alarm signal and to cause an immediate idle down.

The microprocessor is also programmed to analyze the output of thepressure transducer 68 over a period of time which is longer than theresponse time of the pressure transducer. The analyses performed by themicroprocessor signals when a non-transient flow rate condition of airfrom the main reservoir 64 into the relay valve 66 exists with amagnitude below threshold 84 but with sufficient duration to requireidle down. The invention is not limited to any particular mathematicalanalysis technique for analyzing the output of transducer 68 as afunction of time. A first form of mathematical analysis which may beused to analyze the output of the pressure transducer is to integratethe area underneath the curve traced by the output of the pressuretransducer from the beginning of an analysis time interval (12 secondsin FIG. 14) to the end of the analysis time interval (28 seconds in FIG.14). Preferably with the present invention, but not limited thereto, asixteen second time interval is used as an integration time basis. Whenthe value of the integration over the sixteen second time intervalexceeds a second threshold, the microprocessor signals the presence of acondition requiring idle down. In situations where trains are leavingrailroad yards early in the morning under low temperature conditions, itis common for jolting caused by the starting of the cars to producetransients in the brake pipe 22 consequent from the couplings beingmoved with respect to each other. With the prior art system which wasonly sensitive to the absolute magnitude of the differential pressureacross the pressure transducer, cold conditions would at times causeundesired idle down. The present invention averages transients with theremainder of the output of the differential pressure transducer 68 byanalyzing the output of the pressure transducer over a period of timelonger than the response time of the pressure transducer. Themicroprocessor in the remote unit 12 is programmed to cause itsassociated transceiver 28 to signal the lead unit 14 that a significantflow of air is occurring into the brake pipe 22 from the main reservoirat the remote unit.

In addition, the communications channel between the remote units 12 andthe lead unit 14 may be used as a mechanism for checking the continuityof the brake pipe 22 at the initiation of operation of the train 18. Thecontinuity check is performed by applying the air brakes at the leadunit without air brake application at the remote unit and determining ifthe remote unit senses a significant flow rate of air through the flowadapter 70 within 20 seconds of the application of the brakes by thelead unit. If the application is not sensed, the remote unit 12 will nottransmit a significant brake flow alarm which signals the engineer inthe lead unit 14 that the brake pipe 22 does not have continuity andthat the remote unit 12 cannot be operated to power the train.

As an alternative to the integration of the output of the differentialpressure transducer 68, the microprocessor may be programmed inaccordance with known programming techniques to arithmetically averagethe differential pressure over a period of time larger than the responsetime of the differential pressure transducer for calculating a numericalvalue which may be used to indicate whether or not a significant flowrate exists from the main reservoir 64 to the relay valve 66 which isnot susceptible to being erroneously exceeded by transient conditions.

As another alternative to the integration of the output signal from thedifferential pressure transducer, the output of the differentialpressure transducer may be averaged over a plurality of subtimeintervals within a larger time interval of analysis to signal when apredetermined number of the averages during the subtime intervalsconsecutively exceed a threshold. This analysis, like the two preceedinganalysis is not subject to being erroneously affected by transients.

Thus in accordance with the present invention the effects of transientconditions which do not require remote idle down of the air brakes areeliminated which has been a problem with the prior art mechanicalpressure transducers which analyzed flow rate. Moreover, the ability toanalyze the flow rate from both an absolute maximum pressuredifferential and a lower time averaged pressure differential providesthe train control system with the ability to differentiate response tothose conditions which require the instantaneous initiation of idle downand the initiation of idle down after an analysis for a period of time.

FIG. 6 illustrates the details of the automatic brake manifold 74 ofFIG. 5 which in conjunction with the microprocessor control systemfunctions to maintain a specified equalizing reservoir pressureconsequent from the activation of the air brake console controls 44 bythe engineer in the lead unit 14. An automatic brake application isinitiated by pressing an automatic application button within air brakeconsole 44 of FIG. 3 which causes operation of magnet valves which aredescribed below. The pressures in the lead unit and remote unitequalizing reservoirs 82 are reduced equally as long as the automaticbrake application button is pressed for more than 1.5 seconds. The firstreduction is 7 psi which is caused by activation of the automatic valveup to 1.5 seconds and the reductions thereafter are 2 psi (minimum) perstep. The lead unit 14 automatic brake function is discussed infra withregard to FIG. 9 and the remote automatic brake function is discussedinfra with regard to FIG. 11. The equalizing reservoir pressureregulating valve 86 is part of the automatic air brake control value.The equalizing reservoir pressure regulating valve 86 is coupled tomicroprocessor 88 via a pressure transducer 106 in the automatic brakemanifold 74. A magnet valve 90, which has a first input port 92 coupledto the brake valve, a second input port 94 coupled to the atmosphere 96by choke 97 and an output port 98, functions to selectively apply inputpressurized air from the brake valve or exhaust air through the outputport. A fast rate magnetic valve 100 has an input port 102 coupled tothe output port 98 of the solenoid valve 90 and an output port 104coupled to pressure transducer 106 and the equalizing reservoir 82. Thepressure transducer 106 is coupled to the microprocessor 88 forproviding the microprocessor with the pressure of the equalizingreservoir 82. A slow rate magnetic valve 108 has an input port 110 whichis coupled to the output port 98 of the magnet valve 90 via a choke 112and an output port 114 coupled to the equalizing reservoir via choke116. The chokes 112 and 116 function to reduce the flow rate through theslow rate magnetic valve 108 below the flow rate into the fast ratemagnetic valve 100. Preferably, the slow rate magnetic valve is the onlyone of the magnetic valves activated when a comparison of the desiredpressure in the equalizing reservoir and the actual pressure read by thepressure transducer 106 by the microprocessor is less than plus or minus1.0 but greater than + 0.2 psi. When the difference between the pressureread by the pressure transducer 106 and the specified air pressure isgreater than plus or minus 1.0 psi, both the fast rate magnetic valve108 and the slow rate magnetic valve 100 are opened. The pressureregulator of FIG. 6 functions under the program control of themicroprocessor 88 to apply the air from the brake valve via the magnetvalve 90 to the equalizing reservoir when the pressure read by thepressure transducer 106 is less than the pressure commanded by theautomatic brake valve 78 and couples the atmospheric pressure 96 to theequalizing reservoir 82 when the pressure read by the pressuretransducer 106 is greater the pressure commanded by the automatic brakevalve. The magnitude of the pressure differential is analyzed asdescribed above to selectively activate either the slow rate magnetvalve 108 alone when the error is less than +1.0 psi but greater than0.2 psi or the combination of the slow rate magnet valve 108 and thefast rate magnet valve 100 when the pressure differential between thepressure dictated by the automatic brake valve and that read by thepressure transducer 106 is greater than +1.0 psi. As has been discussedabove with reference to the prior art, an unregulated equalizingreservoir is subject to thermal variation caused by ambient temperatureconditions. When a train goes from a cold area to a warmer area such asa tunnel, the resultant pressure rise in the equalizing reservoir 82caused by the thermal absorption of energy from the warmer interior ofthe tunnel could cause a degraded braking operation when the tunnel hasa downhill grade. Alternatively, the entrance of the train into a tunnelin a summertime condition when the tunnel would be cooler than theexterior of the tunnel may produce a pressure drop in the equalizingreservoir 82 consequent from the thermal flow of heat from theequalizing reservoir which could cause an automatic braking of the trainrequiring the units to work against the increased braking force beingapplied by the air brakes or in the extreme cause the train to stopwhich requires extensive preparation for restarting the train. Theregulated equalizing reservoir of the present invention eliminates theseproblems and provides for the maintenance of the desired air pressure inthe equalizing reservoir substantially independent of thermal conditionsor leaks.

V. Communications

The four main types of radio communications in the system are (1) linkmessage, (2) link reply message, (3) commands from the lead unit 14requesting control functions in the one or more remote units 12 and (4)status and alarm messages transmitted by the one or more remote unitswhich update or provide the lead unit 14 with necessary operatinginformation concerning the one or more remote units. These four types ofmessages insure a secure transmission link which has a low probabilityof being interferred with by communications transmitted from other unitswithin radio transmission distance, provides complete control of theremote units 12 and provides complete information of the remote unitoperation including responses to any controls originating from the leadunit 14.

All communications which originate in the lead station 30 and the one ormore remote stations 32, off board repeater 26 and control tower 16 areunder the control of a microprocessor controller located at each ofthese locations. Each individual station microprocessor is programmed toprocess the information required to generate communications for thatstation mode (lead or remote). If the stations are changeable from alead to a remote by activation of appropriate control, themicroprocessor of each station is programmed to assume either stationmode. If a station is programmed to function as a lead station 30, themicroprocessor is programmed to generate the link message and thecommands to be transmitted to the remote units 14. If the station isprogrammed to operate as a remote station 32, the microprocessor isprogrammed to generate the link reply message and the status and alarmmessages. All communications are in the form of a multibyte serialformat which is transmitted on the previously described FSK modulated FMcarrier. The bit positions in each byte convey information regardingdifferent control conditions, alarms or addressing of the stations. Eachof the bytes listed below, includes the usual start (0) and stop (1)bits and the odd parity check bit. These bits have been left out forpurposes of simplifying the disclosure.

    __________________________________________________________________________    1. Common Format                                                              Byte #                                                                            Bit #                                                                             Bit Value                                                                          Functional Description of Message Format                         __________________________________________________________________________    1   0   0    Barker Code, byte 1                                                  1   0    The barker code is used to verify that a received trans-             2   1    mission is information instead of noise. The probability             3   1    of the barker code occurring randomly is small and                   4   1    therefore its detection is indicative of the receipt of              5   0    information.                                                         6   1                                                                         7   1                                                                     2   0   0    Barker Code, byte 2                                                  1   0                                                                         2   0                                                                         3   1                                                                         4   0                                                                         5   1                                                                         6   1                                                                         7   0                                                                     3   0   2**0 Byte Count Byte                                                      1   2**1 The byte count indicates the number of data bytes to                 2   2**2 follow.                                                              3   2**3                                                                      4   2**4                                                                      5   2**5                                                                      6   not used                                                                  7   not used                                                              4   0   2**0 Origin Code Byte                                                     1   2**1 The origin code indicates any of eight possible                      2   2**2 originating locations of a message, i.e., lead unit,                          remote #1, remote # 2, tower control, etc.                       4   3   2**0 Repeat Code                                                          4   2**1 The repeat code indicates any of three possible repeat                        modes and direct transmission. The repeat modes are                           (1) repeated by remote #1, (2) repeated by off board                          repeater 26, and (3) repeated by remote #1 and off board                      repeater 26.                                                         5   2**0 Message Type Code                                                    6   2**1 The message type code indicates any of eight possible                7   2**2 message types. Only four types are described herein; link,                    link reply, lead command and remote status and alarm.            5   0   2**0 Source Unit Address Code, Byte 1                                     1   2**1 The source unit address code is the serial number of the             2   2**2 station, i.e., lead or remote station identification                 3   2**3 number. The source unit address is the second unique                 4   2**4 identifier of either the lead unit or of the one or                  5   2**5 more remote units.                                                   6   2**6                                                                      7   2**7                                                                  6   0   2**8 Source Unit Address Code, Byte 2                                     1   2**9                                                                      2   2**10                                                                     3   2**11                                                                     4   2**12                                                                     5   2**13                                                                     6   2**14                                                                     7   2**15                                                                 __________________________________________________________________________

    __________________________________________________________________________    2. Individual Format                                                          (a) Link/Unlink Messages. The link message is used for initiating the         establishment of a                                                            radio communication link between a lead unit and one or more remote units     and is                                                                        transmitted from the lead unit as a message addressed to a particular         remote unit.                                                                  The unlink message ends the previously established communication link.        Byte #                                                                            Bit #                                                                             Bit Value                                                                              Lead Unit Identification # Bytes                             __________________________________________________________________________     7  0   2**0     Least Significant Digit                                          1   2**1     The lead unit # is preferably the four digit number              2   2**2     assigned by the railroad for identifying that unit               3   2**3     and is typically visible on the unit. The                                     lead unit # is the first lead unique identifier.                 4   2**0     2nd Digit                                                        5   2**1                                                                      6   2**2                                                                      7   2**3                                                                   8  0   2**0     3rd Digit                                                        1   2**1                                                                      2   2**2                                                                      3   2**3                                                                      4   2**0     4th Digit                                                        5   2**1                                                                      6   2**2                                                                      7   2**3                                                                   9  0   2**0     Remote Unit Identification # Bytes                               1   2**1     Least Significant Digit                                          2   2**2     The remote unit # is preferably the number assigned              3   2**3     by the railroad for identifying that unit and is                              typically visible on the unit. The remote unit # is the                       first remote unique identifier.                               9  4   2**0     2nd Digit                                                        5   2**1                                                                      6   2**2                                                                      7   2**3                                                                  10  0   2**0     3rd Digit                                                        1   2**1                                                                      2   2**2                                                                      3   2**3                                                                      4   2**0                                                                      5   2**1                                                                      6   2**2                                                                      7   2**3                                                                  11  0   2**0     System Version Code Byte                                         1   2**1     The system version code is the third identifier used in          2   2**2     the system which is common to both the remote and lead           3   2**3     units, unlike the lead and remote unit identifiers.              4   2**4     The version code may be thought of as another address                         but                                                              5   2**5     is useful for differentiating message formats                                 associated                                                       6   2**6     with different types of equipment such as diesel or              7   2**7     electric. The version code in the link and link reply                         messages must be in agreement with the stored version                         code                                                                          at the receiving station for the receiving station to                         process the received message.                                12  0   Link Remote #1                                                                         Function Byte                                                    1   Link Remote #2                                                                         The function byte contains a single function                                  identification                                                   2   Not Used used with the link sequence. Only one function can be            3   Unlink Sequence                                                                        transmitted with each link transmission.                             (reverse of link)                                                         4   Not Used                                                                  5   Not Used                                                                  6   Not Used                                                                  7   Not Used                                                              13  0            The vertical parity byte is used in accordance with              1            known techniques and an odd parity bit is generated              2            from the vertical parity byte.                                   3                                                                             4                                                                             5                                                                             6                                                                             7                                                                         __________________________________________________________________________    (b) Link Reply Message. The link reply message is used for establishing a     radio communication                                                           link between a lead unit and one or more remote units and is transmitted      from the remote                                                               unit addressed by the link message in response to the link message. The       first,                                                                        second and third identifiers contained in the link reply message must         agree with the first,                                                         second and third identifiers which are stored at the lead unit for that       lead unit to                                                                  complete establishment of the communication link over which all               subsequent messages will                                                      be transmitted.                                                               Byte #                                                                            Bit #                                                                             Bit Value                                                                              Lead Unit Identification # Bytes                             __________________________________________________________________________     7  0   2**0     Least Significant Digit                                          1   2**1     The lead unit # is preferably the four digit number                           assigned                                                         2   2**2     by the railroad for identifying that unit and is                              typically                                                        3   2**3     visible on the unit. The lead unit # is the first lead                        unique identifier.                                               4   2**0     2nd Digit                                                        5   2**1                                                                      6   2**2                                                                      7   2**3                                                                   8  0   2**0     3rd Digit                                                        1   2**1                                                                      2   2**2                                                                      3   2**3                                                                      4   2**0     4th Digit                                                        5   2**1                                                                      6   2**2                                                                      7   2**3                                                                   9  0   2**0     Least Significant Digit                                          1   2**1     The remote unit # is preferably the four digit number            2   2**2     assigned by the railroad for identifying that unit               3   2**3     and is typically visible on the unit.                            4   2**0     2nd Digit                                                        5   2**1                                                                      6   2**2                                                                  10  0   2**0     3rd Digit                                                        1   2**1                                                                      2   2**2                                                                      3   2**3                                                                      4   2**0     4th Digit                                                        5   2**1                                                                      6   2**2                                                                      7   2**3                                                                  11  0   2**0     System Version Code Byte                                         1   2**1     The system version code is the third identifier used in                       the                                                              2   2**2     system which is common to both the remote and lead                            units                                                            3   2**3     unlike the lead and remote unit identifiers which are                         uniquely                                                         4   2**4     assigned to each unit. The version code may be thought           5   2**5     of as another address but is useful for differentiating          6   2**6     message formats associated with different types of                            equipment                                                        7   2**7     such as diesel or electric. The version code in the link                      and                                                                           link reply messages must be in agreement with the                             stored                                                                        version code at the receiving station for the receiving                       station to process the received message.                     12  0   Link Remote #1                                                                         Function Byte                                                    1   Link Remote #2                                                                         The function byte contains a single function                                  identification                                                   2   Not Used used with the link sequence. Only one function can be            3   Unlink Sequence                                                                        transmitted with each link transmission.                             (reverse of link)                                                     12  4   Not Used                                                                  5   Not Used                                                                  6   Not Used                                                                  7   Not Used                                                              13  0            Vertical Parity Byte                                             1            The vertical parity byte is used in acordance with                            known                                                            2            techniques and an odd parity bit is generated from the           3            vertical parity byte.                                            4                                                                             5                                                                             6                                                                             7                                                                         __________________________________________________________________________    (c) Command Messages. The command messages are the control functions that     a lead unit can                                                               specify a remote unit to perform and include the whole range of               operations which                                                              could be performed by an engineer in a remote unit. In a command, a           particular bit is                                                             used if the control function is "yes" or "no" or a combination of bits        are used if                                                                   different degrees of control are possible, e.g., unit traction mode where     eight throttle                                                                settings are used. Each command contains all of the current functions to      be performed                                                                  at the instant of transmission.                                               Byte #                                                                            Bit #                                                                             Bit Value                                                                              Lead Function Control Bytes                                  __________________________________________________________________________     7  0   2**0     Analog multiplexer bits                                          1   2**1     These four bits are used to command the display of                            analog                                                           2   2**2     quantities of the operation of a remote unit on the                           console                                                          3   2**3     and are used preferably for the display of (1) flow                           rate                                                             4   Not Used data of air flow into the brake pipe of a remote                              locomotive 12                                                    5   Not Used (FIGS. 6 and 14), (2) equalizing reservoir pressure                           (FIGS. 5                                                         6   Not Used and (6), (3) brake pipe pressure (FIG. 5) and (4) brake                       cylinder pressure.                                               7            Change radio select bit                                                       This bit commands that radio transmitter be changed to                        the                                                                           remaining backup transmitter.                                 8  0   ER       Engine run enabling function                                     1   GF       Generator field for traction mode                                2   B        Brake (electric)                                                 3   BG       Brake Set-up                                                     4   FO       Forward direction                                                5   RE       Reverse direction                                                6   MS       Ground Relay Reset. This bit resets the electrical               7   GRR      ground detector in the remote unit.                           9  0   2**0     Traction/brake bits                                              1   2**1     These are the eight possible throttle settings                   2   2**2                                                                      3   DV       Engine shut-down                                                 4   FV       Feed value in                                                                 This enables remote brake pipe charging.                         5   ISO      Isolate command bit                                                           This bit disables the remote unit from responding to                          engine and airbrake commands. Alarm functions are                             transmitted.                                                     6   Not Used                                                                  7   Not Used                                                              10  0   2**0     These bits control independent application of unit                            brakes.                                                          1   2**1     The unit brakes are energizable in sixteen 800 m. sec.           2   2**2     intervals up to 12.5 seconds duration.                           3   2**3                                                                      4   IBR      Independent brake release. This bit releases the                              independent brakes.                                              5   Not Used                                                                  6   Not Used                                                                  7   EBA      Emergency application of air brakes. Full braking                             applied                                                                       to air brakes and the unit to be placed in the idle                           state.                                                       11  0   2**0     Automatic application of air brakes. A specified                              pressure                                                         1   2**1     in the equalizing reservoir is established with each             2   2**2     automatic brake application (FIG. 9) from a first 7 psi          3   2**3     reduction to successive one-half pound intervals.                4   2**4                                                                      5   2**5                                                                      6   2**6                                                                      7   ABR      Automatic release/emergency reset commands full release                       of train brakes.                                             12               Vertical Parity                                                               The vertical parity byte is used in accordance with                           known techniques and an odd parity bit is generated                           from the vertical byte parity.                               __________________________________________________________________________    (d) Status/Alarm Messages. The status/alarm messages are the response to      lead unit commands                                                            and alarm conditions that a remote unit transmits to the leads unit for       conveying                                                                     information of remote unit performance which requires prompt atention by      the                                                                           engineer in the lead unit.                                                    Byte #                                                                            Bit #                                                                             Bit Value                                                                              Remote Unit Operations                                       __________________________________________________________________________     7  0   2**0     Analog multiplexer bits                                          1   2**1     These bits are used to display analog quantities of the          2   2**2     operation of a remote locomotive as specified in a                            command                                                          3   2**3     message from the lead unit message.                              4   WARN     Remote System Warning. This bit signals non-fatal                             system                                                                        failures, such as power supply performance drop.                 5   FAIL     Remote System Fail. This bit signals total system                             failure,                                                                      such as failure of the air brakes or DIA converter.              6            Communication Check Request. This bit requests a                              communication check of the radio channel from the lead                        unit.                                                         7  7   SRB      Alternative Radio Selected. This bit signals activation                       of the backup radio.                                          8  0   ER       Engine Run                                                       1   GF       Generator Field                                                  2   B        Brake                                                            3   BG       Brake Set-up                                                     4   FO       Forward direction                                                5   RE       Reverse direction                                                6   MS       Sand applied                                                     7   GRR      Ground Relay Reset                                                            These bits signal various remote unit engine                                  conditions.                                                   9  0   2**0     Traction/brake                                                   1   2**1     These bits signal which of the eight possible traction/          2   2**2     brake conditions have been selected.                             3   DV       Engine Shut-down. This bit signals remote engine                              shut-down.                                                       4   FV       Feed value in. This bit signals charging of the brake                         pipe                                                                          by a remote unit.                                                5   ISO      Isolate. This bit signals placing of a remote unit in                         isolate                                                          6   Not Used                                                                  7            Invalid Traction Step. This bit signals an invalid                            throttle setting.                                            10               Function Acknowledge Bits                                        0            Traction/Dynamic Brake Change                                    1            Operating Step Change                                            2            Feed valve                                                       3            Independent Brake Application                                    4            Independent Brake Release                                        5            Automatic Application                                            6            Automatic Release/Emergency                                      7            Emergency Application of Brakes                                               These bits acknowledge remote performance.                   11  0   2**0     Remote Unit Operations                                           1   2**1     These bits control the digital read-out in the lead                           unit                                                             2   2**2     console.                                                         3   2**3                                                                      4   2**4                                                                      5   2**5                                                                      6   2**6                                                                      7   2**7                                                                  12               Alarms                                                           0   BW       Brake Warning                                                    1   SG       General                                                          2   GR       Ground Relay                                                     3   PC       PC Trip                                                          4   Not Used                                                                  5   Not Used                                                                  6   Not Used                                                                  7   WS       Wheel Slip                                                                    These bits indicate specified alarm conditions in a                           remote unit.                                                 13  0   Not Used                                                                  1            Engine Brakes Applied                                            2            Uncommanded Brake Release which occurs when brake                             pipe pressure rises at least 2 psi.                              3   Not Used                                                                  4            Significant Unexpected flow into brake pipe at remote                         unit.                                                            5   Not Used                                                                  6   Not Used                                                                  7   Not Used                                                              14               Vertical Parity Byte                                                          The vertical parity byte is used in accordance with                           known                                                                         techniques and an odd parity bit is generated from the                        vertical byte.                                               __________________________________________________________________________

VI. Microprocessor Programs

FIG. 7 illustrates the sequence of programs which are individuallyprocessed asynchronously with respect to each other by each of themicroprocessors 54 located respectively at the lead unit 14 and the oneor more remote units 12. It should be understood that FIG. 7 is acomposite of the programs which are executed by both the lead and theremote station microprocessors. The section of programs to the left inFIG. 7, which is identified by the legend "lead" are the programsexecuted by the lead station 30 and the section of programs to the rightin FIG. 7, which is identified by the legend "remote" are the programsexecuted by the one or more remote stations 32. Referring to FIG. 7,each control program 200 starts at starting point 202 and proceeds topoint 204 where all hardware in the associated station is initialized. Asystem power on test is provided at point 205, between points 204 and206, to check the operational status of the microprocessor system ofFIG. 4. The program proceeds from point 204 to point 206 where adetermination is made if the station has been designated as a leadstation or a remote station. One way for the designation to be made isby the activation of an appropriate control on the station console 34(FIG. 3). The program proceeds to point 208 where the actualdetermination is made of whether the particular station was designatedas lead or remote.

A. Lead Station Programs

If the station has been designated as a lead station, the programproceeds to point 210 where the subroutine for lead system mode functionis executed. The lead system mode function is described in detail infrawith reference to FIG. 8. The program proceeds from point 210 to point212 where the lead automatic brake function subroutine is processed. Thelead automatic brake function subroutine is described in detail infrawith regard to FIG. 9. The program proceeds from point 212 to point 214where the lead independent brake subroutine is processed. Thissubroutine controls engine brakes in the lead end remote units and isactivated by the push button input described supra from the console 44of the lead unit. The details of the lead independent brake functionsubroutine are not described herein for the reason that they are notnecessary for understanding the present invention. The program proceedsfrom point 214 to point 216 where the lead feed valve functionsubroutine is processed. The lead feed valve function subroutine point216 controls remote feed valve sequencing and the brake pipe continuitytest which is a necessary condition for starting the operation of thetrain after the linking sequence has been completed by the transmissionof the link and link reply messages. In the lead feed valve functionsubroutine 216, after the application of an automatic brake applicationby the train engineer to the lead unit 14, the program searches for aradio communication message from each of the one or more remote units 12which signals that a significant flow rate has been sensed by the flowsensor of FIG. 5 located at each remote unit. If no radio communicationis received from any of the one or more remote units 12, the leadstation interprets the absence of the radio communication as a brakepipe discontinuity which is a serious condition under which the trainshould not be operated. The program proceeds from point 216 to point 218where the lead status function subroutine is executed. The lead statusfunction subroutine point 218 reads inputs from the various sensors inthe lead unit, stores those inputs and processes the inputs as necessaryfor system operation. The details of the lead independent brake functionsubroutine 218 are not described herein for the reason that they are notnecessary for understanding the present invention. The program proceedsfrom point 218 to point 220 where the console communication functionsubroutine is executed. The function of the console communicationsfunction subroutine is to perform input-output functions for the console34 in the lead station. The details of the console communicationfunction subroutine 220 are not described herein for the reason thatthey are not necessary for understanding the invention. The programproceeds from point 220 to point 222 where the lead events recordingfunction subroutine is executed. The lead events recording functionsubroutine 222 is an optional digital recording function of systemoperation which stores various parameters of system operation in therandom access memory which may be contained within the processing board54 of FIG. 4 and provides a printed output for later analysis. Theprogram proceeds from point 222 to point 224 where the systemdiagnostics subroutine is executed for determining the operability ofvarious parts of the system. The details of the system diagnosticssubroutine 224 are not described herein for the reason that they are notnecessary for understanding the invention.

B. Remote Stations

If the station is a remote station, the program proceeds from point 208to point 226 where the remote system mode function subroutine isexecuted. The details of the remote system function subroutine 226 aredescribed infra with regard to FIG. 10. The program proceeds from point226 to point 228 where the remote automatic brake function subroutine isexecuted. The details of the remote automatic brake function subroutine228 are described infra in conjunction with FIG. 11. The programproceeds from point 228 to point 230 where the remote independent brakefunction subroutine is executed. The function of the remote independentbrake function subroutine point 230 is to execute the control functionsdictated by the lead independent brake function subroutine (point 214)after appropriate commands have been received via the communicationchannel between the lead unit 14 and the remote unit 12. The details ofthe remote independent brake function subroutine 230 are not describedherein for the reason that they are not necessary for understanding theinvention. The program proceeds from point 230 to point 232 where theremote feed valve function subroutine is executed. The remote feed valvefunction subroutine 232 executes the control functions dictated by thelead feed valve function subroutine (point 216) after the commands havebeen received over the radio communication channel between the lead unit14 and the remote unit 12. The details of the remote feed valve functionsubroutine 232 are not described herein for the reason that they are notnecessary for understanding the invention. The program proceeds frompoint 232 to point 234 where the remote status function subroutine isexecuted. The remote status function subroutine 234, processes messagesfrom the lead locomototive 14 requesting data, reads the data, andtransmits the data to the lead unit. The remote status functionsubroutine 234 also executes engine commands. The details of the remotestatus function subroutine 234 are not described herein for the reasonthat they are not necessary for understanding the invention. The programproceeds from point 234 to the remote events recording functionsubroutine 236 which is an optional digital recording function of systemoperation analogous to that described with reference to the lead eventsrecording function subroutine (point 222). The program proceeds frompoint 236 to point 238 where the system diagnostics subroutine isexecuted for checking the operability of the various parts of thesystem. The details of the system diagnostics subroutine 238 are notdescribed herein for the reason that they are not necessary forunderstanding the invention.

It should be understood that the microprocessor cycles through theforegoing subroutines repeatedly and executes various parts of thesubroutines on a real time basis as the necessary conditions permittingtheir execution occur.

C. Lead Station Mode Function Program

FIG. 8 illustrates the microprocessor control flow chart for theexecution of the linking function by the lead station 30. The entirelinking function by the lead station 30 includes the generation of thelink message and the processing of the link reply messages generated bythe one or more remote units 12 and the subsequent generation of acommand which establishes the communication link between the lead unit14 and one of the remote units. The program starts at point 300 andproceeds to decision point 302 where a determination is made if the leadunit 14 is linked. If the answer is "yes", the program proceeds todecision point 304 where a determination is made if a new automaticbrake application has been made. A new automatic brake application isthe execution of the engineers' brake command by the activation of theautomatic brake pushbutton on the brake console 44 in FIG. 3. If theanswer is "yes", the program proceeds to point 306 where a communicationcheck software timer is set for five seconds. The communication checktimer is used to check the system communications during an automaticbrake application. If the remote(s) do not reply (with an automaticbrake application acknowledge bit set) within 5 seconds, a communicationinterruption alarm is displayed on the console. The program proceedsfrom point 306 to point 308 where a determination is made if thecommunication check timer started at point 306 is zero. If the timer hasreached zero, the program proceeds to point 310 where a communicationinterruption message is flashed on a control console 34 of the lead unit14. If the communication check timer is not equal to zero, the programbranches from point 308 bypassing point 310 to point 312 where thelatest remote status message is checked for the unexpected significantair flow bit. If the answer is "yes", the program proceeds to point 314where the system enters the control mode which permits the remote unit12 to cooperate with the lead unit 14 to move the train. If a remoteflow was not detected at decision point 312, the program bypasses thesystem mode control point 314 to point 316 where the unit controls areread to determine if they are set in an improper operational mode, e.g.,dynamic brakes and throttle applied at the same time or the lead unitset in forward and reverse, etc. The program proceeds from point 316 topoint 318 where a determination is made if any command interlocks infact do exist. If the answer is "yes", the program proceeds to point 320where the next command message to be transmitted is adjusted toeliminate the improper conditions. If the answer is "no" at decisionpoint 318, the program proceeds to return point 322 while bypassing thecommand message adjustment point 320 previously described. The returnpoint 322 herein and in the ensuring description of the remainingsubroutines is to the main program where the next subroutine is entered.The previously described sequence of program steps resulting from a"yes" determination at point 302 is for the purpose of detecting if thetrain 18 is in the linked or control state. If the determination atpoint 302 was "no", the program proceeds to the section where thebeginning of linking is initiated at point 324. At point 324 the trainis set in the isolate condition with the emergency brakes applied whichprevents movement of the train until the linking sequence is completed.The program proceeds from point 324 to point 326 where a determinationis made if the appropriate control on the control console 34 of the leadunit 14 has been activated to request linking with a particular remoteunit 12. It should be understood at this juncture that the addressselect switches of box 56 located on the lead console 34 have beenactivated to store the remote unit numbers (first unique remoteidentifiers) to which the lead unit 14 is to be linked and that theremote units have their link unit number switches of box 56 set to storethe first identifier of the lead unit. If the answer is "no" at decisionpoint 326, the program returns to the next subroutine via the returnpoint 322. If the answer is "yes" at decision point 326, the programproceeds to decision point 328 where the program has three differentbranch options based on the state of the software link timer. The firstbranch option is when the link timer is inactive which occurs only whenthe link command has been initially given from the console 34 in thelead station 30. The program proceeds from decision point 328 in theinactive state to point 330 where the link message request is given. Thelink message request point activates the transceiver 28 of the lead unit14 to produce a link message with the format described above under thecommunications section. The program proceeds from point 330 to point 332where the link timer is initialized and started. The program proceedsfrom block 332 to the return point 322. The timing out interval for thelink timer is five seconds. If five seconds have elapsed, the programproceeds from point 328 to point 334 where the appropriate indicator onthe console is lited to signal a link alarm. The program proceeds frompoint 334 to point 336 where the link timer is placed in the inactivestate as described above. The .program proceeds from point 336 to thereturn 322 as described above. If the link timer is active at decisionpoint 328, the program proceeds to decision point 338 where adetermination is made if a link reply message has been received by thelead unit station 30. If a link reply message has not been received, theprogram branches to return point 322. If a link reply message has beenreceived, the program branches to point 340 where a comparison is madeof the stored first unique identifiers of the lead and remote units andthe version code (third identifier) with the first lead and remoteidentifiers and version code contained in the received link replymessage. The program proceeds to decision point 342 where the results ofthe comparison are checked. If the comparison at point 342 is notidentical, the program proceeds to the return point 322. If thecomparison at point 342 of the first identifiers and the version code isidentical, the program proceeds to point 344 where the second uniqueidentifier contained in the link reply message is stored in memory ofthe lead station 30 for use in addressing the remote unit 12 for allfuture commands to be transmitted by the lead unit 14 after the linkingsequence is completed. The program proceeds from point 344 to point 346where the system enters the linked mode. The receipt of the firstregular command after the saving of the second unique identifier atpoint 344 confirms the establishment of the communication link betweenthe lead unit 14 and that remote unit 12. The program proceeds frompoint 346 to return point 322.

D. Lead Station Automatic Brake Function

FIG. 9 illustrates a flow chart of the microprocessor control programfor the lead unit automatic brake function. The program proceeds fromstarting point 400 to decision point 402 where a determination is madeif the emergency brakes for the train are to be set. If the answer is"yes", the program proceeds to point 404 where the emergency brakes atthe lead unit 12 are set by deactivating the emergency solenoid valve inthe lead unit. The program proceeds from point 404 to point 406 where acommand message is transmitted from the lead unit 14 to the remote units12 requesting the setting of the emergency brakes in the remote units.The format of the command message is that specified supra with regard tocommand messages in the communication section. The program proceeds frompoint 406 to point 408 where the system operation is changed to the idlemode which disables the lead unit 14 from transmitting any controlfunctions. The program proceeds from point 408 to decision point 410where a determination is made if a release of the automatic brakes hasbeen requested. If the answer is "yes", the program proceeds to point412 where the air pressure regulation system of FIGS. 5 and 6 outputsmaximum air pressure to the equalizing reservoir 82 causing the airbrakes to be fully released. The program then proceeds from point 412 topoint 414 where the pneumatics are cleared and reset for both theautomatic brake function and the emergency brake function. The programproceeds from point 414 to point 416 where a determination is made ifthere is an automatic brake application present. If the answer is "no",the program proceeds to point 418 where a determination is made if acontinuous reduction is being made. If the answer is "yes", the programproceeds to decision point 420 where a determination is made if thebutton for requesting automatic brake application on the automatic brakeconsole 44 has just been released. If the answer is "yes" at decisionpoint 420,, the program proceeds to point 422 where the pressure readingby the pressure transducer 106 of FIG. 6 is inputted. The programproceeds from point 422 to point 424 where one p.s.i. is substractedfrom the specified equalizing reservoir pressure. The program proceedsfrom point 424 to point 426 where the new equalizing reservoir controlpressure is outputted to the lead station 30 for the maintenance of theequalizing reservoir 82 at a new pressure. The program proceeds frompoint 426 to point 428 where the calculation is made of the newequalizing reservoir pressure for the remote units 12. The remoteequalizing reservoir pressure reduction at point 428 is equal to thedifference between the maximum lead equalizing reservoir pressure andthe current lead equalizing reservoir pressure. If the answer was "no"at decision point 418, the program proceeds to decision point 430 wherea determination is made if a penalty brake application is required.Typical penalty conditions include an overspeed condition of the unit, adead man control in the unit is not activated or the lead brake valvecontrol has been moved out of the release position. If the answer is"yes", the program proceeds to point 432 where the equalizing reservoirpressure to be applied by the remote unit is set to cause maximumbraking upon the transmission of the next command. The program proceedsfrom point 432 to point 434 where an output of 0 p.s.i. is transmittedto the equalizing reservoir control which allows the equalizingreservoir to fall at its maximum programmed rate. The program proceedsfrom point 434 to return point 436 which returns the program to theexecution of the next subroutine in the master flow chart of FIG. 7. Ifthe answer at decision point 430 was "no", the program proceeds directlyto the return point 436. If the determination at decision point 416 was"yes" that there was an automatic brake application request, the programproceeds to decision point 438. The determination at decision point 438is "yes" each time the automatic brake button in the lead unit ispushed. If the decision at point 438 is "no", the program proceeds todecision point 440 where a determination is made if the timer for theautomatic brake application is equal to zero and active. If the answeris "yes" at decision point 440 which indicates that the automatic brakeapplication timer has timed out, the program proceeds to point 442 where0 psi is outputted to the equalizing reservoir pressure regulationcontrol which allows the equalizing reservoir to fall at its maximumprogrammed rate. The program proceeds from point 442 to point 444 wherethe automatic brake application timer is inactivated. The programproceeds from point 444 to decision point 430 as previously described.If the answer was "no" at decision point 440, the program proceedsdirectly to decision point 430 as described. If the answer was "yes" atdecision point 438 that there was a new automatic application of the airbrakes, the program proceeds to decision point 446 where a determinationis made if the application was the first application. If the applicationwas determined to be the first application (from a release condition) atdecision point 446, the program proceeds to point 448 where the pressurein the equalizing reservoir 82 is read from the pressure transducer 106of FIG. 6. This is saved as the maximum equalizing reservoir pressure.The program proceeds from point 448 to point 450 where 7 psi issubstracted from the maximum equalizing reservoir pressure. The programproceeds from point 450 to point 452 where the 7 psi drop specified forthe lead unit at point 450 is set for application at the remote unit 12.The 7 psi drop for the remote unit 12 is transmitted to the remote unitduring the next command message. The program proceeds from point 452 topoint 454 where the automatic brake application timer is set for 2seconds and the timer is started to run. The program then proceeds topoint 456 where the new pressure dictated by the setting of theautomatic brake valve 78 is outputted to lower the pressure in theequalizing reservoir 82 to the desired pressure by the appropriateapplication of control signals to the valves of the pressure regulationapparatus of FIG. 6. The program proceeds from point 456 to thepreviously described decision point 430. If the answer was "no" atdecision point 446 that the application of the automatic brakes was notthe first application, the program proceeds to point 458 where 2 psi issubtracted from the pressure of the equalizing reservoir of the leadunit 14 which is currently being maintained. This drop in pressure willapply the brakes harder. The program proceeds to point 460 where thespecified 2 psi pressure drop in the lead unit 14 is translated to therequested pressure of the equalizing reservoir of the remote unit 12.The two pound pressure drop specified at point 460 is transmitted to theremote units at the next command message. The program proceeds frompoint 460 to point 462 where the automatic brake application timer isset equal to one second and the timer is started. The timer enables acontinuous reduction in equalizing reservoir pressure only after thebutton has been pressed for 1 second. The one second interval issufficient to drop the equalizing reservoir approximately 2 psi.Thereafter the program proceeds to point 456 as previously described.

E. Remote Station Mode Program

FIG. 10 illustrates a flow chart of the microprocessor program of theremote stations 32 for processing communications and remote functions.The program starts at starting point 500 and preceeds to decision point502 where a determination is made if the system is linked. If the systemis linked (or in control mode), the program proceeds to decision point504 where a determination is made if an unlink message, described abovein section V with reference to the link message (byte 12, bit 3) hasbeen received. If the answer is "yes" at decision point 504, the programproceeds to point 506 where the system is unlinked. At point 506 theelectronic controls of the remote station 32 are reset to prepare thesystem for another linking sequence. The program proceeds from point 506to point 508 where the remote units 12 are set in the isolate mode withthe emergency brakes applied. In the isolate mode, the remote unit 12may not execute any commands from a lead unit 14. The program proceedsfrom point 508 to point 510 where the remote unit 12 requests thetransmission of a reply message to the lead unit 14 acknowledging thereceipt of the unlink request. The program proceeds to return point 512where it returns to the main program to execute the next subroutine. Ifthe answer was "no" at decision point 504, the program proceeds todecision point 514 where a determination is made if there is acommunication interruption. A communication interruption is defined as aforty five second gap since the receipt of the last message from thelead unit 14. Normally, the lead unit 14 transmits at least every twentyseconds which prevents the timing out of the forty five second timer. Ifthere has been a communications interruption detected at decision point514, the program proceeds to decision point 516 where a determination ismade if a sufficient air flow has been detected at the remote station 32by the flow rate analyzier of FIG. 5 as discussed supra. When thecommunications channel is out between the lead unit 14 and the remoteunit 12, a significant air flow is interpreted as a lead unit brakeapplication which requires a remote idle-down and cut-out of the freedvalve thereby allowing the brakes to be fully applied. The programproceeds from decision point 516 is a significant air flow has beendetected to point 518 where the feed valve is moved to the out position.The program proceeds to decision point 520 where the determination ismade if the feed valve is out. If the feed valve is out, a programproceeds to decision point 522 where a determination is made if theremote unit 14 is in the traction mode. If the answer is "yes" atdecision point 522, the program proceeds to point 524 where the remoteunit is placed in the die condition. The program proceeds from point 524to point 512 which is a return to the main program. If the answer was"no" at decision point 514, the program bypasses the previouslydescribed sections of the program and proceeds directly to point 526,where a determination is made if any functional interlocks exists by theactivation of inconsistent control functions such as the application ofhigh throttle settings and high dynamic braking or the lead unit 14being in forward and the remote units 12 being in reverse, etc. If theanswer was "no" at decision point 520, the program proceeds directly topoint 512. If the answer was "no" at decision point 522, the programproceeds directly to point 512. The program proceeds from point 526 todecision point 528 where the actual determination is made if anyfunctional interlocks exist. If the answer is "yes" at decision point528, the program proceeds to point 530 where the various controlfunctions are adjusted to remove the interlock condition and theoperation of the remote unit is sequenced into the requested condition.If the answer was "no" at decision point 528, the program proceedsdirectly to return point 512. The program also proceeds to return point512 from point 530. If the answer was "no" at decision point 502, theprogram proceeds to point 532 where the remote unit is placed in theisolate condition with the emergency brakes applied. The isolatecondition disables all unit control functions with the emergency brakesapplied. The program proceeds from point 532 to decision point 534 wherea determination is made if a link command has been received. If theanswer is "yes", the program proceeds to point 536 where a comparison ismade of the stored first identifiers of the lead and remote unit andversion code with the first lead and remote identifiers and the versioncode contained in the link message. The program proceeds from point 536to point 538 where a determination is made if the first identifiers andthe third identifier (version code) are identical. If the answer is"yes" at point 538, the program proceeds to point 540 where the secondunique identifier (serial number of lead station 30) is stored in theRAM memory of the remote station 32. The program proceeds to point 542where a request is made for the remote station to transmit a link replymessage. The program proceeds from point 542 to point 544 where the linktimer is set equal to five seconds. The function of the link timer is todetect if a command message is received by the remote station withinfive seconds which is required to complete the linking sequence. If thetimer times out in five seconds, the linking sequence is aborted. If theanswer at decision point 534 was "no", the program proceeds to decisionpoint 546 where a determination is made if a command message from a leadunit 14 was received. If the answer is "yes", the program proceeds todecision point 548 where a determination is made if the link timer isactive. The link timer is active only one time between the receipt of alink message and the receipt of a command from the lead unit 14 aftertransmission of the link reply message which completes the linksequence. If the answer is "yes" at decision point 548, the programproceeds to decision point 550 where the system is changed from thesystem mode and the link timer is turned off. The program proceeds frompoint 550 to return point 512. If the answer was "no" at decision point546 or decision point 548, the program proceeds directly to return point512.

F. Remote Station Automatic Brake Function

FIG. 11 illustrates the flow chart of the microprocessor remote stationautomatic brake function program. The program proceeds from startingpoint 600 to decision point 602 where a determination is made if acommand has been made to activate the emergency brakes in the remoteunit 12. If the answer is "yes", the program proceeds to point 604 wherethe appropriate controls are set for activating the emergency brakes atthe remote unit. The program proceeds to point 606 where the variousunit controls are placed in the idle mode. If the answer is "no" atdecision point 602, the program proceeds to decision point 608 where adetermination is made if there has been an automatic brake release. Ifthe answer is "yes" at point 608, the program proceeds to point 610where the maximum air pressure commanded in the equalizing reservoir 82is set in the memory for maintaining a specified equalizing reservoirpressure. The microprocessor control acts on the specification of amaximum equalizing reservoir pressure to cause the release of theautomatic brakes. The program proceeds from point 610 to point 612 wherethe emergency brakes are reset. If the answer was "no" at decision point608 that there had not been an automatic brake release, the programproceeds to decision point 614 where a determination is made if therehas been an automatic application of the air brakes at the remote unit.The program proceeds from point 612 to decision point 614. If the answeris "no" at decision point 614, the program proceeds to return point 616where the program returns to the main program to process anothersubroutine. The program proceeds from decision point 614 to decisionpoint 618 where determination is made if the automatic application ofthe air brakes detected above at decision point 614 was the firstautomatic application of the air brakes. If the answer is "yes" at point618, the program proceeds to decision point 620 where the equalizingreservoir pressure read by the pressure transducer 106 of FIG. 6 isinputted. The program proceeds from point 620 to point 622 where thespecified air pressure reduction contained in the automatic brakeapplication is subtracted from the stored value of the pressure whichwas being maintained in the equalizing reservoir by the pressureregulator. The program proceeds from point 622 to point 624 where thespecified pressure is outputted to cause the equalizing reservoir toassume the new lower pressure contained in the stored value of thedesired equalizing pressure. The program proceeds from point 624 toreturn point 616. If the answer was "no" at decision point 618, theprogram proceeds to point 626 where a comparison is made of the newlyspecified equalizing reservoir pressure reduction (application code)with the previously specified equalizing reservoir pressure reduction.If the newly specified pressure reduction results in an actual rise inequalizing pressure, it is not allowed. A graduated release of airbrakes caused by an increase in air pressure is not allowed becausedifferent cars release their air brakes at different pressures andrates. Thus all air brake releases must be by the application of maximumbrake pipe pressure. The program proceeds from point 626 to decisionpoint 628 where the actual determination is made if the newly specifiedequalizing reservoir pressure reduction is greater than the previouslyspecified equalizing pressure reduction. If the newly specifiedequalizing reservoir pressure reduction is greater than the previouspressure reduction, the program proceeds to the previously describedpoint 622 where the new pressure reduction is subtracted rom the maximumpressure. If the answer is "no" at decision point 628, the programproceeds to return point 616.

G. Linking Sequence

FIG. 12 temporally illustrates the sequence of communications whichoccurred during the linking sequence. The linking sequence is started inan unlinked condition by the pressing of the link buttons on the controlconsole 34 of the lead unit 14 as indicated at point 700. The programproceeds from point 700 to point 702 where the formatting of the linkmessage in accordance with the format discussed supra in the section Vis accomplished. The program proceeds from point 702 to point 704 wherethe previously formatted link message is transmitted from the lead unit14. Each of the one or more remote units 12 receives the transmittedlink message at point 706. Thereafter at point 708, the stored firstunique identifiers of the lead and remote unit and the third identifierare compared with the received first unique identifiers and the thirdidentifier. At point 710 a determination is made if the variousidentifiers are in agreement. If the answer is "no", the remote unitremains in the unlinked condition as indicated by point 712. If thecomparison does agree, the remote unit 12 saves the second uniqueidentifier contained in the link message and starts the link timer asindicated at point 714. The remote unit next formats and transmits alink reply message of a format as discussed supra in the section V atpoint 716. After the transmission of the link reply message by theremote unit 12, the lead unit 14 receives the link reply message atpoint 722. The lead unit 14 at point 724 compares the stored first leadand remote unique identifiers and the third identifier with the receivedfirst unique lead and remote identifiers and the third identifier. Ifthe determination at point 726 is different, the lead station 30 ignoresthe communication. If the comparison at point 726 of the identifiersagrees, the lead station 30 proceeds to point 728 where the secondunique identifier contained in the link reply message is saved for thepurpose of checking the addressing in the later status/alarm generatedby the remote station. The lead station 30 is set in the linked mode atpoint 730. Thereafter at point 732, the lead unit 734 transmits acommand message to the remote unit 14 which sent the link reply message.The function of this command message is twofold in that one it transmitsa command which should be processed by the remote unit 12 and is alsointerpreted by the remote unit as completing the link sequence. At point734 the remote unit 14 receives a command message. The second uniqueidentifier contained in the command message is compared at point 736with the previously stored second unique identifier of the lead unit 14which was stored at point 714. If the comparison does not agree, themessage is discarded at point 738. If the comparison does agree, themessage is conveyed to the decoding section of the microprocessorcontrol as indicated at point 740. At point 742 the remote unit 12 isnow set in the link mode which indicates that the linking sequence iscomplete. At point 744 the remote unit formats an appropriate responseto the command message and transmits a status or alarm message to thelead unit 14 which sent the message to the remote unit as indicated atpoint 732. At point 746 the lead unit 14 receives the status or alarmmessage which was transmitted by the remote unit at point 744. At point746 a comparison is made between the second unique identifier containedin the status or alarm message transmitted by the remote unit 12 withthe second unique identifier stored in the memory of the lead station30. If the second unique identifiers agree, the lead unit proceeds withprocessing the received status or alarm message. Thereaftercommunications proceed between the lead and remote units.

H. Brake Pipe Continuity Test

FIG. 13 illustrates the brake pipe continuity test which is executed bythe present invention to determine if the train air brakes are incondition for safe operation. At point 800, which occurs after linking,an automatic brake application request is made by the operator. At point802 a signal is sent to the remote unit such as by the application ofthe automatic air brakes at the lead unit. But no transmission of theautomatic brakes application is made by the lead station 30. This beginsthe continuity check sequence. Alternatively, other signals as, forexample, air brake perturbation signals could be applied. A timer is setat point 804 which begins running at the time of application of thebrakes at the lead unit 14. The timer continues to run at decision point806. If the timer times out consequent from not receiving a radiocommunication from the remote units 12, a link alarm is activated on theunit console 34 at point 808. At the remote unit which has beenpreviously linked, the flow rate input from the flow sensor of FIG. 6 isread at point 810. The sensed flow rate data is analyzied at point 812by the remote station microprocessor. A decision is made at decisionpoint 814 if a significant flow rate has been sensed in accordance withthe criteria discussed above with reference to FIGS. 6 and 13. At point816 an appropriate alarm message is formatted and transmitted to thelead unit 14 if a significant flow rate was detected.

At the lead unit the alarm message is received at point 818. If theanalysis of the second unique identifier of the remote unit 12 iscorrect at point 820, the lead unit formats and transmits a brakeapplication message at point 822 and proceeds into the control mode atpoint 824. In the control mode, the system is free to operate in anymanner specified by the engineer in the lead unit 14. The remote unit 12receives the command message formatted at point 822 at point 826. Aftera determination at point 828 that the second unique identifier containedin the message agrees with the stored second unique identifier, theremote unit acts on the command message at point 830. At point 832 theremote unit 12 transmits an appropriate status message to the lead unit14. At point 834 the lead unit receives the status message and proceedsto analyze its address at point 836. Thereafter, the operation of thetrain proceeds under the control of the engineer in the lead unit 14with the radio communication channel transmitting information betweenthe lead and remote units 14 and 12.

VII. Communication Channel Contention

The communication system of the present invention minimizes interferenceon the same communication channel caused by stations within multipletrains and stations within the same train. Preferrably, a combination offixed and randomized time intervals measured from the end of the latesttransmission are assigned for making the various types of communicationsin the system. The preferred system for determining transmission timesfor all types transmissions in the system is set forth below in tableform. It should be understood that the priority system is not limited tothe specific combination of fixed and randomized time intervals.

    ______________________________________                                        Time of Transmission Measured form End                                        of Transmission of Latest Transmission                                                               Time Transmissions                                                            Within Time                                            Types of Communications                                                                              Interval                                               ______________________________________                                        I.   Fixed priorities, fixed time                                                                        80-360 ms                                               intervals spaced at least 40 ms                                               apart. These communications                                                   are the highest priority                                                      transmissions in the system.                                                  Reply of remote #1 to command                                                                       (1) 80 ms                                               of lead unit.                                                                 Reply of Remote #2 to command                                                                       (2) 120 ms                                              of lead unit.                                                                 Operation of on board (1) 80 ms                                               repeater in remote #1                                                         Operation of off board                                                                              (3) 360 ms                                         II.  High Priority Commands,                                                                             400-520 ms                                              4 randomized intervals.                                                                             (1) 400 ms                                              Any command is assigned                                                                             (2) 440 ms                                              a randomized time period                                                                            (3) 480 ms                                              (m = 4) within the 400-520 ms                                                                       (4) 520 ms                                              time interval by a random                                                     number generator programmed                                                   in the station microprocessor                                                 counting from l to m.                                                         High priority commands include:                                          1.     Emergency Brake Application                                            2.     Automatic Brake Application                                            3.     Remote Station Initiated                                                      Communications Checks &                                                       Responses by Lead Station                                              4.     Remote Station Alarms                                                  5.     Remote Status Change                                                   6.     Link/Unlink Messages                                                   III. Lead Locomotive Commands                                                                            560 ms-840 ms                                           (except Automatic Brake                                                                             (1) 560 ms                                              Application and Emergency                                                                           (2) 660 ms                                              Brake Application), 8 randomized                                                                    (3) 640 ms                                              levels. Any command is                                                                              (4) 680 ms                                              assigned a randomized time                                                                          (5) 720 ms                                              period (n = 8) within the                                                                           (6) 760 ms                                              560-840 ms time interval by a                                                                       (7) 800 ms                                              random number generator                                                                             (8) 840 ms                                              programmed in the microprocessor                                              counting from l to n.                                                    IV.  Lead Locomotive Communications                                                                      880 ms-1160 ms                                          Checks, 8 randomized levels                                                                         (1) 880 ms                                              The lead unit communica-                                                                            (2) 920 ms                                              tions check, which is broadcast                                                                     (3) 960 ms                                              after a period of sustained                                                                         (4) 1000 ms                                             silence by any remote unit                                                                          (5) 1040 ms                                             transceiver, is assigned                                                                            (6) 1050 ms                                             a randomized time period (p = 8)                                                                    (7) 1120 ms                                             within the 880-1160 ms time                                                                         (8) 1160 ms                                             interval by a random number                                                   generator programmed in the                                                   microprocessor counting from l to p.                                     V.   Lead Locomotive Communications                                                                      1200 ms-1480 ms                                         During a Period of Communication                                                                    (1) 1200 ms                                             Interruption, 8 randomized levels                                                                   (2) 1240 ms                                             A message from the lead unit                                                                        (3) 1280 ms                                             during a period when a communica-                                                                   (4) 1320 ms                                             tion interruption has been                                                                          (5) 1360 ms                                             detected consequent from                                                                            (6) 1400 ms                                             sustained radio silence is                                                                          (7) 1440 ms                                             assigned randomized time period                                                                     (8) 1480 ms                                             (r = 8) within the 1200-1480 ms                                               time interval by a random number                                              generator programmed in the                                                   microprocessor counting from l to r.                                     ______________________________________                                    

The random time periods within the four categories of transmissionsdescribed above are generated in each station microprocessor by onerandom number generator counting between one and the number of timeperiods within the time interval during which individual transmissionscan occur. The programming of a computer to generate a random numberwithin a counting sequence is known. The count of the random numbergenerator at the end of the latest transmission is used to calculate thetransmission delay count based on the current status of the station. Thedelay begins immediately when a transmission is required to be made. Ifthe timer is still running, the transmission is delayed. If the timerhas run out, the transmission proceeds. For example, assuming that thesystem has a high priority command waiting for transmission, and therandom number generator (counting between 1 and m) count for determininghigh priority commands is a 3 at the end of the latest transmission, anautomatic brake application command (the high priority command) would betransmitted 480 ms after the end of the latest transmission was detectedby the lead station regardless of whether that transmission was from astation within the same train 18 or from another train system withinradio transmitting distance. Similarly all other stations within thevarious systems would have chosen random number values and transmissiondelay times at the end of the latest transmission. Each time atransmission occurs over the radio communication channel, the timeintervals for determining transmission discussed above are restarted andthe various number generators are set. Each station makes itstransmission on a real time basis as soon as the condition warrantingthe transmission has occured and the requisite time interval of radiochannel silence has elapsed from the latest transmission on the channel.The primary principle of operation of the channel contention system isthat the first unit station to begin transmitting prevents the otherstations from transmitting as a consequence of the above describedtransmission time determining system in which the time interval of radiochannel silence is begun again.

While the preferred channel contention system utilizes fixedtransmission times for transmissions of the highest priority,alternatively the highest priority transmissions may be assigned randomtime intervals by using a random number generator which counts from 1 toq. The assignment of the time of transmission for each remote unit replyand repeater transmission is controlled by the random number generatorsuch that the times of transmission of each remote unit and therepeaters are assigned randomly to the 40 ms time intervals within the30-360 ms time of transmission.

While the preferred form of the second unique identifier is the stationserial number, it should be understood that the second uniqueidentifiers may alternatively be generated by the microprocessor locatedat each lead and remote station by a random number generator inaccordance with known programming principles. The randomly generatedsecond unique identifier would be stored in the RAM of each station andused in the same manner described above.

While the foregoing invention has been described in terms of itspreferred embodiments, it should be understood that variousmodifications may be made thereto without departing from the spirit andscope of the invention as defined in the appended claims. It is intendedthat all such modifications fall within the scope of the appendedclaims.

What is claimed is:
 1. In a communication system for use with thecontrol of a railroad train having a plurality of transceivers, thetransceivers being located on lead and remote units of the train, a leadunit controlling the operation of a remote unit by way of a transmissionwhich includes a command transmitted by a lead transceiver over acommunication channel therebetween, a remote unit transmitting a replyto a command confirming execution of the command, and informationrepresentative of the operation of a remote unit, a system forcontrolling which unit transmits on the channel comprising:at eachrespective unit, first means, associated with the transceiver of thatunit, for detecting the ending of the latest transmission by anytransceiver on the communication channel; and second means, coupled tosaid first means, for causing its associated transceiver to initiate atransmission upon the termination of the delay of a prescribed period oftime after the detection of the ending of said latest transmission bysaid first means, and wherein each transmission over said communicationchannel is prioritized into one of a plurality of different ranges oftime delay that must terminate before that transmission may beinitiated, such that a higher priority transmission is initiated after atime delay that is shorter than any time delay within a range of timedelays of a lower priority transmission.
 2. A system according to claim1, wherein, within a respective range of time delays into which atransmission is prioritized, the time delay that must expire before atransmission is initiated is randomly selected.
 3. A system according toclaim 2, further comprising:a second repeater at a location other thanon the train for receiving transmissions from a lead or remote unit andretransmitting such transmissions, said second repeater having atransceiver the initiation of transmission from which is prioritizedinto a range of time delay that follows the range of time delay intowhich retransmission of a message by the first repeater is prioritized.4. A system according to claim 1, wherein a remote unit functions as arepeater for receiving a transmitted message from a lead unit andretransmitting that message, and wherein the time delay that must expirebefore the remote unit retransmits the message is the same as that fortransmitting a reply to a transmission from the lead unit.